[Elecraft] Re: KX1 Part 1 problems? - Regulator

Sun Nov 2 10:25:00 2003

Hi Wayne and Gang

When building my KX1 I used a LP2950CZ5.0 voltage regulator in place of =
the LM78L05. I have been using this part for years in a device a I =
manufacture. The LM78L05 has about 3 mA  of quiescent current used up in =
the part alone while the 2950 uses only 90 uA,  the output voltage =
tolerance is better (1% I think) and it only needs .5 volt of overhead. =
For a battery powered device saving 3 mA is significant when the total =
current draw is around 32 mA. This could mean a 10% increase in battery =
life. The only problem I had was I needed to add a bypass capacitor near =
the regulator. I was getting .5 volt of noise on the 5 volt buss. I =
added a 0.1 uF mono cap across the regulator output and ground soldered =
to the regulator pads on the back of the board. The noise was causing =
the S-meter and battery voltage to read erratic. The cap fixed it. This =
may also happen with the LM78L05 although I think the 2950 is more =
susceptible to oscillation if the bypass is not right at the output =
pins. Anyway I just thought I would pass this along.=20

Don Brown
KD5NDB

  ----- Original Message -----=20
  From: Wayne Burdick=20
  To: [email protected]=20
  Cc: [email protected]=20
  Sent: Friday, October 31, 2003 11:39 PM
  Subject: [Elecraft] Re: KX1 Part 1 problems?

  >=20
  > D2 Anode: reades 126mv AC rms
  > D2 Cathode: Reads 116mv AC rms
  >=20
  > Both are over the recommended 20mv AC rms. The instructions say that =
this
  > indicates that one of the voltage regulators is oscillating, but I =
can't
  > figure out what the troubleshooting should be. Any ideas?

  You may be picking up 60 Hz AC noise on your probes, Paul. What does =
the meter
  read if you put *both* probes on the same lead of each diode?

  If you think the reading is "real", you might have a problem with a =
voltage
  regulator. Usually this would be due to an unsoldered pin on an =
electrolytic
  cap, or one installed backwards.

  73,
  Wayne
  N6KR

  --=20

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